Package structure and packaging method

ABSTRACT

A package structure includes: a heat dissipation substrate; at least one die, including a signal transmitting side and a heat conduction side, wherein the signal transmitting side and the heat conduction side are two opposite sides on the die, and the heat conduction side is disposed on and in contact with the heat dissipation substrate; plural metal bumps, disposed on the signal transmitting side; and a package material, encapsulating the die, a side of the heat dissipation substrate in contact with the die, and the metal bumps, wherein a portion of each metal bump is exposed to an outside of the package material.

CROSS REFERENCE

The present invention claims priority to provisional application63/282,574 filed on Nov. 23, 2021, and TW 111102577 filed on Jan. 21,2022.

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates to a package structure, especially apackage structure wherein a die is not connected to a lead frame so thatthe parasitic resistance and inductance are reduced, and as such thelead frame can even be omitted.

Description of Related Art

FIG. 1 shows a package structure 100 in a quad flat no lead (“QFN”hereinafter) package is shown, which is one typical packaging method toencapsulate a die 101. This packaging method uses a lead frame 102 as acarrier structure, wherein a die 101 is attached to the lead frame 102by soldering. The lead frame 102 and the die 101 thereon areencapsulated by a package material (or molding compound) 104; and thenthe encapsulated die 101 and lead frame 102 are cut into an individualpackage unit, that is, plural package units are manufacturedconcurrently and each of which includes the die 101 and the lead frame102. The die 101 in the QFN package communicate with its outside throughthe exposed portions of the lead frame 102.

There is a problem that the QFN package needs to face. The lead frame102 may cause high parasitic resistance and high parasitic inductanceduring transmitting signals. Referring to FIG. 2 , when the circuitstarts operating, a ringing effect occurs due to the parasiticresistance and inductance of the lead frame 102, and this can last forquite a long time to result in a delay in signal transmission. Theparasitic inductance will increase the impedance even more significantlywhen transmitting high frequency signals, and the ringing effect becomeseven more noticeable under a high current condition.

Referring to FIG. 3 , in order to overcome this problem, a priorapproach is to do circuit optimization by circuit analysis software, tostraighten the right-angle turns in the lead frame for shortening thesignal communication length, so as to reduce the parasitic resistanceand inductance thereof.

Regarding heat dissipation in the package structure, a typical prior artapproach is to dispose an additional heat dissipation material on thedie on the lead frame to enhance the heat dissipation capability. Forinstance, FIG. 4 shows the package structure 10 of U.S. Pat. No.7,812,437; FIG. 5 shows the package structure 20 of U.S. Pat. No.7,164,210; and FIG. 6 shows the package structure 30 of U.S. Pat. No.7,560,309. In these patents, the dies 11, 21, and 31 are disposed on thelead frames 12, 22, and 32, which are encapsulated by the packagematerials 14, 24, and 34, correspondingly; and the heat dissipationmaterials 15, 25, and 35 are disposed on the dies 11, 21, and 31,correspondingly. In manufacturing the package structures 10, 20, and 30,the heat dissipation materials 15, 25, and 35 are disposed after thedies 11, 21, and 31 are disposed on the lead frames 12, 22, and 32.These disposition processes are complicated and any error during theseprocesses can cause the cooling effect of dies 11, 21, and 31 to bedowngraded. Besides, the problem of the aforementioned high parasiticresistance and inductance still remains and is not solved by these priorarts.

In view of the aforementioned drawback in the prior arts, the presentinvention provides a package structure wherein the lead frame is omittedto significantly reduce the parasitic resistance and inductance causedby the lead frame, and further to provide a high heat dissipationefficiency in the package structure.

SUMMARY OF THE INVENTION

In one perspective, the present invention provides a package structure,which can greatly reduce the parasitic resistance and inductance ascompared to the prior art, and at the same time have the performance ofhigh heat dissipation efficiency. The package structure of the presentinvention includes: a heat dissipation substrate; at least one die, eachdie including a signal transmitting side and a heat conduction side,wherein the signal transmitting side and the heat conduction side aretwo opposite side to each other, and the heat conduction side isdisposed on and in contact with the heat dissipation substrate; aplurality of metal bumps, disposed on the signal transmitting side; anda package material, encapsulating the die, a side of the heatdissipation substrate in contact with the die, and the metal bumps,wherein a portion of each metal bump is exposed outside the packagematerial.

In one embodiment, the signal transmitting side has no signal connectionwith the lead frame.

In one embodiment, the heat dissipation substrate is made of a highthermal conductive material.

In one embodiment, the heat dissipation substrate has aside which isexposed to the outside of the package structure, and this exposed sidehas a planar shape, a wavy surface, or has a matrix of one or moregeometric shapes.

In one embodiment, a heat dissipation path between the die and theoutside of the package structure is formed through the heat conductionside of the die and the heat dissipation substrate, to transfer a heatenergy generated by the die to the outside of the package structure.

In one embodiment, the metal bumps are electrically connected to anexternal circuit board or a redistribution layer.

In one embodiment, the metal bumps are fabricated by an electroplatingprocess or a ball mounting process. The material of the metal bumpsincludes a metal, an alloy, or a composite material structure.

In one embodiment, the package structure includes a plurality of dies,wherein the metal bumps are disposed on the signal transmitting sides ofthe dies, and the heat conduction sides of the dies are disposed on theheat dissipation substrate.

In one embodiment, the package structure further includes a plurality ofrouting lines disposed on the package material for transmitting signalsbetween the metal bumps. The package structure further includes a stackpackage layer to encapsulate the routing lines and the package material.

In one perspective, the present invention provides a package method,which includes: providing at least one die, each die including a signaltransmitting side and a heat conduction side, wherein the signaltransmitting side and the heat conduction side are two opposite side toeach other; disposing a plurality of metal bumps on the signaltransmitting side; disposing a heat dissipation substrate under and incontact with the heat conduction side; providing a package material toencapsulate the at least one die on the heat dissipation substrate andto encapsulate the metal bumps; and after the step of providing apackage material to encapsulate the at least one die on the heatdissipation substrate and to encapsulate the metal bumps, cutting toseparate the at least one die, the heat dissipation substrate and themetal bumps from other portions to form at least one package unit,wherein each package unit includes the at least one die, the metalbumps, a post-cut heat dissipation substrate, and a post-cut packagematerial.

In one embodiment, the aforementioned at least one die includes: a die,a plurality of dies, or a plurality of dies on a wafer.

In one embodiment, the at least one die includes a plurality of dies,wherein the metal bumps are disposed in the signal transmitting side ofeach die, and the heat conduction side of each die is disposed on theheat dissipation substrate; wherein the package method further includes:disposing a plurality of routing lines on the package material torespectively connect the metal bumps; and disposing a stack packagelayer to encapsulate the routing lines on the package material.

In one embodiment, after the step of providing a package material toencapsulate the at least one die on the heat dissipation substrate andto encapsulate the metal bumps, the package method further includes:grinding the package material and the metal bumps; and performing areflow step to recover tops of the metal bumps.

In one embodiment, the heat dissipation substrate is disposed on acarrier layer, and the package method further includes: after eachpackage unit is formed, removing the package unit from the carrierlayer.

The objectives, technical details, features, and effects of the presentinvention will be better understood with regard to the detaileddescription of the embodiments below, with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 6 show several prior art package structures.

FIG. 7 shows a package structure according to one embodiment of thepresent invention.

FIGS. 8 and 9A to 9E respectively show heat dissipation substratesaccording to several embodiments of the present invention.

FIGS. 10A to 10C show dies and metal bumps according to severalembodiments of the present invention.

FIG. 11 shows a package structure according to one embodiment of thepresent invention.

FIGS. 12A to 12D show steps in the package method according to oneembodiment of the present invention.

FIGS. 13A to 13E show steps in the package method according to oneembodiment of the present invention.

FIGS. 14A to 14F show steps of the package method according to oneembodiment of the present invention.

FIG. 15 shows a comparison table of electrical characteristics betweenthe prior art and the present invention.

FIG. 16 shows a thermal resistance comparison between the prior art andthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings as referred to throughout the description of the presentinvention are for illustration only, to show the interrelations betweenthe components or units, but not drawn according to actual scale ofsizes.

Compared with the prior packaging technology, the present inventionomits the lead frame, so that the package structure has lower parasiticresistance and inductance. The heat dissipation substrate provides bothfunctions for disposing the die and for heat dissipation, so that thepackage structure and the manufacturing process are simplified while thesignal transmission efficiency is improved.

FIG. 7 shows a package structure 40 according to an aspect of thepresent invention, the package structure 40 including: a heatdissipation substrate 41, at least one die 42, a plurality of metalbumps 43 and a package material 44. Each die 42 includes a signaltransmitting side 421 and a heat conduction side 422, wherein the signaloutput side 421 and the heat conduction side 422 are opposite sides toeach other on the die (for example, in FIG. 7 , the signal transmittingside 421 and the heat conduction side 422 are the top side and thebottom side of the die 42, respectively), and the heat conduction side422 are disposed on the heat dissipation substrate 41 (different fromthe prior art wherein the die is disposed on the lead frame, the die 42of the present invention is disposed on the heat dissipation substrate41 in an up-side-down fashion). The plurality of metal bumps 43 aredisposed on the signal transmitting side 421, whereby the die 42 in thepackage structure 40 can transmit and receive signals through the metalbumps 43 in communication with outside of the package structure 40. Thepackage material 44 encapsulates the die 42, a side of the heatdissipation substrate 41 which is connected to the die 42, and the metalbumps 43. One side of each metal bumps 43 is exposed to the outside ofthe package material 41. FIG. 7 shows a package structure including onedie. According to the present invention, a package structure can includemultiple dies, which will be illustrated in other embodiments.

In the prior art, the lead frame needs to provide both functions ofsignal transmission and heat dissipation, that is, the signaltransmitting side and the heat conduction side of the die are on thesame side. In the present invention, the signal transmitting side 421and the heat conduction side 422 of the die 42, are not on the same sideof the die 42, but on opposite sides to each other. The signaltransmitting side 421 has no signal connection with the lead frame. Insome embodiments of the present invention, the package structure doesnot include the lead frame.

In one embodiment, the heat dissipation substrate 41 is made of a highthermal conductive material. The material of the heat dissipationsubstrate 41 can include a metal (for example, copper or aluminum), aceramic material, an alloy (for example, aluminum copper alloy), or acomposite structure (for example, nickel-coated copper, orgraphene-coated copper plate).

In some embodiments, a side of the heat dissipation substrate 41 exposedto the outside of the package structure 40 (that is, the side oppositeto the side of the heat dissipation substrate 41 connected to the die42) is of a planar shape (for example: plane with a solid body, or planewith hollow pipes under (FIG. 8 )); a wavy surface; or a matrix ofspecific geometric shapes (geometric shapes such as: extending arc shape(FIG. 9A), extending square shape (FIG. 9B), extending triangle shape(FIG. 9C), conical protrusion shape (FIG. 9D), square protrusion shape(FIG. 9E), cylinder shape, etc.). These surface designs of the heatdissipation substrate can increase the contact surface of the heatdissipation substrate 41 to the outside, to improve the heat dissipationperformance.

In one embodiment, a heat dissipation path between the die 42 and theoutside of the package structure 40 is formed through the heatdissipation substrate 41 and the heat conduction side 422 of the die 42,to transfer the heat energy generated by the die 42 to the outside ofthe package structure 40. Thus, besides reducing the parasiticresistance and inductance, the package structure 40 according to thepresent invention further has a better heat dissipation effect over theprior art package structure with lead frame. The material, thickness orshape of the heat dissipation substrate 41 can be flexibly determined toachieve a much better heat conduction and heat transfer efficiency, ascompared to the prior art lead frame technology which is relatively morelimited under the manufacturing requirements.

In embodiments as shown in FIGS. 10A, 10B, and 10C, in a projection ofthe signal transmitting side 421 of the die 42 along a verticaldirection V, the metal bumps 43 may include various geometric shapes,such as: square (FIG. 10A), circle (FIG. 10B), ellipse (FIG. 10C),polygon, etc., which can be determined according to manufacturing orsignal wiring requirements.

In one embodiment as shown by the package structure 50 of FIG. 11 , themetal bumps 43 can be electrically connected to an external circuitboard 45 (or a flexible circuit board), or a redistribution layer. Whenthe metal bumps 43 are arranged in a dense layout, a redistributionlayer or an external circuit board can be added to adjust the pitch ofthe layout for better signal contacts with external circuitry.

In embodiments as shown in FIGS. 7 and 11 , a package material 44 fillsthe gaps or space between the metal bumps 43. From one perspective, atleast a portion of the signal transmitting side 421 between the metalbumps 43 is filled with the package material 44.

In one embodiment, the metal bump 43 can be fabricated on the signaltransmitting side 421 by an electroplating process or a ball mountingprocess. The material of the metal bumps 43 can include: metal (forexample, tin, or copper), alloys (for example, tin silver alloy, or tinlead alloy), or composite structure (for example, copper in combinationwith tin silver alloy).

The package structure of the present invention can be applied to modifythe prior art QFN package structure, and other prior art packagestructures. The aforementioned QFN package is one example for thismodification, and the application of the present invention is notlimited to the QFN package; any package structure with lead frame can bemodified according to the present invention to omit the lead frame, andto use the heat dissipation substrate as proposed by the presentinvention.

In one perspective, FIGS. 12A to 12D provide a package method, whichincludes: providing at least one die 42 (FIG. 12A, wherein eight diesare shown as an example), each die 42 including a signal transmittingside 421 and a heat conduction side 422, and disposing a plurality ofmetal bumps 43 on the signal transmitting side 421, wherein the metalbumps 43 can be one same shape or multiple different shapes; disposing aheat dissipation substrate 41 on (or under, from the illustration viewof the drawing) and connected to the heat conduction side 422 of the die42 (FIG. 12B); providing a package material 44 to encapsulate the atleast one die 42 on the heat dissipation substrate 41 and to encapsulatethe metal bumps 43, wherein one side of each of the metal bumps 43 isexposed outside the package material 44 (FIG. 12C); and cutting toseparate the at least one die 42, the metal bumps 43 and the heatdissipation substrate 41 (arrows illustrate the cutting afterencapsulating the package material 44, FIG. 12D) from other portions toform at least one package unit PU (FIG. 12D shows an example of cuttingto form eight package units PU). Each package unit PU includes the die42, the metal bumps 43, a post-cut heat dissipation substrate, and apost-cut package material.

In one embodiment, when the heat dissipation substrate 41 is a flexiblematerial, the heat dissipation substrate 41 can be pre-disposed on acarrier layer 46 (FIG. 13A). As shown in FIGS. 13B to 13D, the steps ofthe package method provided by the present invention further include:providing at least one die 42 (FIG. 13B), each die 42 including a signaltransmitting side 421 and a heat conduction side 422, and disposing aplurality of metal bumps 43 on the signal transmitting side 421, whereinthe metal bumps 43 can be one same shapes or multiple different shapes;disposing a heat dissipation substrate 41 on (or under, from theillustration view of the drawing) and connected to the heat conductionside 422 of the die 42 (FIG. 13C); providing a package material 44 toencapsulate the at least one die 42 on the heat dissipation substrate 41and to encapsulate the metal bumps 43 (FIG. 13D); and afterencapsulating the at least one die 42, cutting to separate (arrowsillustrate the cutting) the metal bumps 43 and the heat dissipationsubstrate 41 from other portions to form at least one package unit PU,and removing each package unit PU from the carrier layer 46 (FIG. 13E).Each package unit PU includes the die 42, the metal bumps 43, a post-cutheat dissipation substrate, and a post-cut package material.

In one embodiment, the at least one die in the package method caninclude: a die, a plurality of dies, or a plurality of dies on a wafer.

In one embodiment, one package unit PU can include multiple dies. In oneembodiment as shown in FIGS. 14A to 14F, the steps of the package methodprovided by the present invention include: providing a plurality of dies42 a, 42 b, and 42 c, and disposing a plurality of metal bumps 43 on thesignal transmitting sides 42 a 1, 42 b 1, and 42 c 1 of the dies 42 a,42 b, and 42 c, respectively, wherein the heat conduction sides 42 a 2,42 b 2 and 42 c 2 of the dies 42 a, 42 b, and 42 c are disposed on andin contact with the heat dissipation substrate 41 (FIG. 14A); providinga package material 44 to encapsulate the dies 42 a, 42 b, and 42 c onthe heat dissipation substrate 41 and to encapsulate the metal bumps 43(FIG. 14B); disposing a plurality of routing lines 47 on the packagematerial 44, to respectively connect the metal bumps 43 (FIG. 14C);disposing a plurality of metal stack bumps 48 on the routing lines 47,to electrically connect the routing lines 47 and/or to electricallyconnect the metal bumps 43 (FIG. 14D); disposing a stack package layer49 to encapsulate the routing lines 47 and the metal stack bump 48 onthe package material 44 (FIG. 14E); and cutting to separate the dies 42a, 42 b, 42 c, the metal bumps 43, the metal stack bumps 48, and theheat dissipation substrate 41 (arrows illustrate the cutting)encapsulated by the package material 44 and the stack package layer 49from other portions, to form plural package units PU. In thisembodiment, each package unit PU includes multiple different dies 42 a,42 b, and 42 c (FIG. 14F), wherein the routing lines provide signalconnections among the dies 42 a, 42 b, and 42 c.

In one embodiment, after the above-mentioned step of encapsulating thedie 42 a, 42 b, 42 c and the metal bumps 43 (or after the step ofencapsulating the stack package layer 49 and the metal stack bumps 48),the exposed surface on the package structure may need to be planarizedby grinding (or polishing). However, this grinding or polishing step maydamage the metal bumps 43 (or the metal stack bumps 48). Therefore,after the aforementioned step of encapsulating the dies 42 a, 42 b, 42 cand the metal bumps 48 (or after the step of encapsulating the stackpackage layer 49 and the metal stack bumps 48), when a step of grindingthe package material 44 and the metal bumps 43 (or grinding the stackpackage layer 49 with metal stack bumps 48) is required, after thegrinding step, a reflow step can be performed to recover the tops of themetal bumps 43 (or the tops of metal stack bumps 48), wherein the topsof the metal bumps or of the metal stack bumps 4843 are tops of exposedto the outside of the package material 44.

FIG. 15 shows a comparison table of electrical characteristics betweenthe prior art and the present invention (the present invention omittingthe lead frame). The comparison results show that the parasiticresistance and inductance of the package structure in the presentinvention are in average 80% lower than that of the QFN package of theprior art, showing that the performance of the present invention is muchimproved over the prior art. Besides, FIG. 16 shows a thermal resistancecomparison between the prior art and the present invention. Thecomparison shows that the thermal resistance in the package of thepresent invention can be 0.9° C./W lower than the package thermalresistance of the prior art QFN package.

The present invention has been described in considerable detail withreference to certain preferred embodiments thereof. It should beunderstood that the description is for illustrative purpose, not forlimiting the broadest scope of the present invention. An embodiment or aclaim of the present invention does not need to achieve all theobjectives or advantages of the present invention. The title andabstract are provided for assisting searches but not for limiting thescope of the present invention. Those skilled in this art can readilyconceive variations and modifications within the spirit of the presentinvention. For example, two or more of the embodiments can be usedtogether, or, a part of one embodiment can be used to replace acorresponding part of another embodiment. For example, the packagestructure is provided with a different number of dies to the drawings,or the components are placed in a different sequence, or the shapes ofthe components are different from the drawings, etc. In view of theforegoing, the spirit of the present invention should cover all such andother modifications and variations, which should be interpreted to fallwithin the scope of the following claims and their equivalents.

What is claimed is:
 1. A package structure, including: a heatdissipation substrate; at least one die, each die including a signaltransmitting side and a heat conduction side, wherein the signaltransmitting side and the heat conduction side are two opposite side toeach other, and the heat conduction side is disposed on and in contactwith the heat dissipation substrate; a plurality of metal bumps,disposed on the signal transmitting side; and a package material,encapsulating the die, a side of the heat dissipation substrate incontact with the die, and the metal bumps, wherein a portion of eachmetal bump is exposed outside the package material.
 2. The packagestructure according to claim 1, wherein the signal transmitting side hasno signal connection with a lead frame.
 3. The package structureaccording to claim 1, wherein the heat dissipation substrate is made ofa high thermal conductive material.
 4. The package structure accordingto claim 3, wherein the material of the heat dissipation substrateincludes a metal, an alloy, or a composite material structure.
 5. Thepackage structure according to claim 3, wherein the heat dissipationsubstrate has a side which is exposed to the outside of the packagestructure, and this exposed side has a planar shape, a wavy surface, orhas a matrix of one or more geometric shapes.
 6. The package structureaccording to claim 3, wherein a heat dissipation path between the dieand the outside of the package structure is formed through the heatconduction side of the die and the heat dissipation substrate, totransfer a heat energy generated by the die to the outside of thepackage structure.
 7. The package structure according to claim 1,wherein the metal bumps are electrically connected to an externalcircuit board or a redistribution layer.
 8. The package structure ofclaim 1, wherein the metal bumps are manufactured by an electroplatingprocess or a ball mounting process.
 9. The package structure accordingto claim 1, wherein the material of the metal bumps includes a metal, analloy, or a composite material structure.
 10. The package structureaccording to claim 1, wherein the at least one die includes a pluralityof dies, wherein the metal bumps are disposed on the signal transmittingside of each die, and the heat conduction side of each die is disposedon the heat dissipation substrate.
 11. The package structure describedin claim 10, further including a plurality of routing lines on thepackage material to connect the metal bumps for transmitting signals,wherein the package structure further includes a stack package layer toencapsulate the routing lines and the package material.
 12. A packagemethod, including: providing at least one die, each die including asignal transmitting side and a heat conduction side, wherein the signaltransmitting side and the heat conduction side are two opposite side toeach other; disposing a plurality of metal bumps on the signaltransmitting side; disposing a heat dissipation substrate under and incontact with the heat conduction side; providing a package material toencapsulate the at least one die on the heat dissipation substrate andto encapsulate the metal bumps; and after the step of providing apackage material to encapsulate the at least one die on the heatdissipation substrate and to encapsulate the metal bumps, cutting toseparate the at least one die, the heat dissipation substrate and themetal bumps from other portions to form at least one package unit,wherein each package unit includes the at least one die, the metalbumps, a post-cut heat dissipation substrate, and a post-cut packagematerial.
 13. The package method of claim 12, wherein the at least onedie includes: a die, a plurality of dies, or a plurality of dies on awafer.
 14. The package method according to claim 12, wherein the atleast one die includes a plurality of dies, wherein the metal bumps aredisposed in the signal transmitting side of each die, and the heatconduction side of each die is disposed on the heat dissipationsubstrate; wherein the package method further includes: disposing aplurality of routing lines on the package material to respectivelyconnect the metal bumps; and disposing a stack package layer toencapsulate the routing lines on the package material.
 15. The packagemethod according to claim 12, wherein after the step of providing apackage material to encapsulate the at least one die on the heatdissipation substrate and to encapsulate the metal bumps, the packagemethod further includes: grinding the package material and the metalbumps; and performing a reflow step to recover tops of the metal bumps.16. The package method according to claim 12, wherein the heatdissipation substrate is disposed on a carrier layer, and the packagemethod further includes: after each package unit is formed, removing thepackage unit from the carrier layer.